Jupiter’s moon Europa has a thick layer of ice on its surface that floats on an ocean. Scientists have now found a possible explanation for the structures on this ice sheet.
Europa is the name of a moon orbiting the giant planet Jupiter. Years ago, astrophysicists discovered with the help of telescopes and space probes that the surface of Europa consists of ice. In this layer, which is probably many kilometers thick, structures can be seen that are interpreted as cracks and faults.
There is also clear evidence that beneath Europa’s outer ice sheet lies a vast ocean of liquid water, and beneath that is a solid, rocky core.
Scientists assume that the ice cover on the Europa Ocean can swim freely, i.e. it can rotate as a hollow sphere on the water surface. Researchers have long had an answer to the obvious question of how temperatures can be so high inside a moon far from the sun under a thick layer of ice that water can exist in liquid form.
On the one hand, the strong gravitational force of the nearby giant planet Jupiter generates tidal forces in the interior of Europa, and thus friction and ultimately heat. The researchers also assume that thermal energy is generated in the core of Europe through the decay of radioactive substances.
Ocean currents on the moon
So far, however, there has been no satisfactory answer to the cracks in the free-floating surface of ice. In the journal “JGR: Planets”, scientists around Hamish Hay from the University of Oxford a surprising explanation for the structures in Europa ice. They had on supercomputers of the Jet Propulsion Laboratory NASA in California simulates the ocean currents in the Europa Ocean.
These are driven by temperature differences. The heat coming from inside the moon heats the water deep in the ocean. There, just as in an earthly cooking pot, warmer water rises to the top because it is less dense.
The researchers used methods also used to model terrestrial seas and expanded them into a large-scale model for Europa’s ocean. They took into account complicated flow-dynamic and temperature-dependent effects as well as the rotation of the moon and tidal forces.
“The result of these simulations is that the currents in the ocean can have an impact on the rotation of the ice sheet,” explains Hay. At first, the currents in the Europa Ocean would run vertically upwards, but then they would acquire more and more a horizontal component and lead to east-west and west-east currents. The study shows that these can be so fast that they can accelerate or decelerate the ice surface.
“For me, this was a completely unexpected result,” comments study co-author and NASA researcher Robert Pappalardo, “it was a big surprise.” This surprise could, however, explain the formation of the cracks in the ice sheet. “Maybe the ocean is to blame,” says Pappalardo. The study raises the possibility that current velocities and directions are changing over time, causing dynamic forces to act on the ice. The visible structures would therefore arise from the stretching and compression of the ice.
If this theory is correct, then the surface structures of Europa should change over time. This in turn can be checked comparatively easily. One only has to compare the Europa photos from previous space missions with those of future missions.
In fact, both Esa and Nasa want to send research probes to Jupiter’s moon Europa. The launch of the Esa probe “Juice” is scheduled for April 13, 2023. In 2024, NASA wants to send “Clipper” towards Europe.
However, the great scientific interest in Jupiter’s moon Europa is not only focused on the structures on its surface. Much more exciting is the question of whether life forms can exist in the ocean under the ice sheet. Neither “Juice” nor “Clipper” will be able to answer this question conclusively. But the researchers are hoping for more pieces of the jigsaw puzzle for an answer.